CN111333064B - High-performance lithium ion battery graphite negative electrode material and preparation method thereof - Google Patents
High-performance lithium ion battery graphite negative electrode material and preparation method thereof Download PDFInfo
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Abstract
The invention provides a high-performance lithium ion battery graphite cathode material and a preparation method thereof, wherein the preparation process comprises the following steps: 1) carrying out surface oxidation treatment on natural graphite; 2) carrying out hard carbon coating on the oxidized natural graphite to obtain a precursor; 3) carbonizing the precursor obtained in the step 2); 4) carrying out juice soaking treatment on the carbonized precursor; 5) and crushing the impregnated material, and then carbonizing to obtain the high-capacity high-power graphite cathode material. The capacity of the natural graphite is improved by surface oxidation treatment, the natural graphite has high-rate charging capacity by hard carbon coating, and the defects left after oxidation and hard carbon coating are repaired by dipping treatment, so that the cycle performance of the natural graphite is improved.
Description
The technical field is as follows:
the invention relates to a graphite cathode material for a lithium ion battery and a preparation method thereof, in particular to a high-performance graphite cathode material for the lithium ion battery and a preparation method thereof.
Background art:
the lithium ion battery mainly comprises a transition metal oxide with lithium embedded in a positive electrode material, a highly graphitized carbon, a diaphragm polyolefin microporous membrane, an electrolyte material and the like as a negative electrode material.
Compared with the traditional lead-acid, nickel-cadmium, nickel-hydrogen and other secondary batteries, the lithium ion secondary battery has the advantages of high working voltage, small volume, light weight, high capacity density, no memory effect, no pollution, small self-discharge, long cycle life and the like. Since some japan successfully commercialize lithium ion batteries in the last century, lithium ion batteries have become the dominant power source for mobile phones, notebook computers, and digital products, and are also increasingly widely used in the fields of electric vehicles, energy storage, and the like. At present, the lithium ion battery cathode material used in large-scale commercialization is mainly a carbon material, mainly comprises natural graphite, artificial graphite and the like, the natural graphite naturally has the advantages of high capacity and high compaction, and the capacity density of the artificial graphite is obviously improved along with the continuous improvement of the artificial graphite technology, and almost reaches the level of the natural graphite
However, at present, the lithium ion battery cathode materials used in large-scale commercialization are mainly carbon materials, including natural graphite, artificial graphite and the like, but the theoretical specific capacity of the lithium ion battery cathode materials is low, about 300mAh/g, and the lithium ion battery cathode materials cannot meet the requirements of high-capacity and high-power lithium ion batteries.
In recent years, especially in the coming of the 5G era, the demand of electronic products on the quick charging performance of batteries is increasing, the negative electrode material is required to meet the 5C charging demand, and the rate performance demand is also increasing. At present, mesophase carbon microspheres, small-particle-size pitch coke, equilateral coke and the like can meet the 5C charging requirement, but the capacity compaction is low, and the capacity density requirement cannot be met. Therefore, there is an urgent need to develop a graphite negative electrode material for a high-capacity high-power lithium ion battery having both the capacity density and the fast charging performance.
For example, in Chinese patent publication No. CN109616639A, a hard carbon-coated expanded microcrystalline graphite material, a preparation method thereof and application thereof in a sodium ion battery are disclosed, in the technology, microcrystalline graphite is used as a base material, and is coated by hard carbon after oxidation, so that the obtained composite material has good conductivity and high sodium storage capacity, but if the composite material is used as a negative electrode material of a lithium ion battery, a large number of micropores of hard carbon exist, electrolyte is easily added into the material through a coating layer, and side reaction occurs, and the cycle performance of the material is influenced. The technology is that a low carbon residue precursor is dispersed in a solvent through a surfactant, then the low carbon precursor is deposited on the surface of an object to be coated through spray drying, then a layer of high carbon residue precursor is uniformly coated on the outer layer of the object, then the coated product is heated and cooled in an inert atmosphere, and finally the elastic carbon material coating structure is obtained through scattering, screening and demagnetizing. The elastic carbon material coating structure prepared by the coating process has strong elasticity, and can avoid cracking caused by violent change of the volume of a coated object. However, the process adopts one-step carbonization, and the hard carbon and soft carbon precursors have the defects of difficult control of the process method and the like in the process of simultaneous carbonization, thereby influencing the performance of the carbonized graphite cathode material.
Therefore, how to provide a high-capacity high-power graphite cathode material for a lithium ion battery and a preparation method thereof can overcome the problems that the capacity compaction of the graphite cathode material for the lithium ion battery is low and the capacity density requirement cannot be met; and simultaneously preparing the graphite cathode material for the high-capacity high-power lithium ion battery with energy density and quick charge performance and the method.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a high-performance graphite cathode material of a lithium ion battery and a preparation method thereof; the capacity is improved by oxidation treatment of natural graphite serving as a raw material, the multiplying power performance is improved by hard carbon coating, the cycle performance is improved by dipping treatment, the capacity is improved by surface oxidation treatment of the natural graphite, the hard carbon coating enables the natural graphite to have high multiplying power charging capacity, defects left after oxidation and hard carbon coating are repaired by dipping treatment, and the cycle performance is improved. The graphite cathode material has low industrial production cost and is used for lithium ion batteries.
The invention aims to provide a preparation method of a high-performance lithium ion battery graphite cathode material, which takes natural graphite as a raw material, improves the capacity through oxidation treatment, improves the multiplying power performance through hard carbon coating, and improves the cycle performance through dipping treatment, and comprises the following steps:
1) the oxidation treatment is to fully stir and mix the natural graphite and the oxidant mixed solution, filter, dry and carry out high-temperature oxidation treatment under the condition of inert atmosphere to obtain oxidized natural graphite;
2) preparing a graphite cathode material precursor, putting the oxidized natural graphite in the step 1) into a coating agent and a corresponding solvent, fully stirring and mixing to obtain a mixture of the oxidized natural graphite and the coating agent, and spray-drying the mixture of the oxidized natural graphite and the coating agent to obtain the graphite cathode material precursor;
3) performing low-temperature carbonization treatment, namely performing low-temperature carbonization treatment on the graphite cathode material precursor obtained in the step 2) in an inert atmosphere to obtain a carbonized graphite cathode material precursor;
4) the pitch dipping treatment, namely placing the carbonized graphite anode material precursor in a pitch solvent, mixing and dissolving under the condition of pressure, taking out, filtering and drying to obtain the pitch carbonized graphite anode material precursor;
5) and (3) carrying out secondary carbonization to prepare the graphite cathode material for the high-performance lithium ion battery, crushing the pitch carbonized graphite cathode material precursor material obtained in the step 4), and then carrying out high-temperature carbonization treatment in an inert atmosphere to obtain the graphite cathode material for the high-performance lithium ion battery.
The preparation method of the high-performance lithium ion battery graphite cathode material comprises the following steps of 1) mixing the oxidant with peroxide and organic acid or inorganic acid, and controlling the mass ratio of natural graphite to peroxide to organic acid or natural graphite to peroxide salt to inorganic acid to be 80-95: 5-20: 1-10; controlling the temperature of the high-temperature oxidation treatment to be 500-600 ℃; the time is 2-4 h.
In the preparation method of the high-performance lithium ion battery graphite cathode material, the coating agent in the step 2) is one or more of sucrose, phenolic resin, epoxy resin and polyvinyl alcohol; controlling the mass ratio of the oxidized natural graphite to the coating agent to be 100: 3-40.
The preparation method of the high-performance lithium ion battery graphite cathode material comprises the step 3) of controlling the temperature of the low-temperature carbonization treatment to be 500-650 ℃, the time to be 6-20h, and controlling the temperature rise rate of the low-temperature carbonization treatment to be 5-8 ℃/min.
The preparation method of the high-performance lithium ion battery graphite cathode material comprises the following steps of 4) asphalt dipping treatment, wherein the asphalt is low-temperature asphalt or medium-temperature asphalt; controlling the pressure to be 0.2-1.5Mp, and keeping the pressure for 0.2-3h under the condition of the pressure.
The preparation method of the graphite cathode material of the high-performance lithium ion battery comprises the steps of 5) controlling the particle size of the material obtained by crushing the pitch carbonized graphite cathode material precursor material to be 1-50 um, controlling the high-temperature carbonization temperature to be 1200-1400 ℃ and the carbonization time to be 5-24 h; controlling the temperature rise rate of high-temperature carbonization to be 4-10 ℃/min.
Preferably, the oxidizing agent is a mixture of sodium persulfate and oxalic acid or a mixture of sodium peroxide and concentrated sulfuric acid.
The graphite cathode material for the high-performance lithium ion battery is prepared by the preparation method of the graphite cathode material for the high-performance lithium ion battery, the graphite cathode material for the high-performance lithium ion battery is formed by coating hard carbon on oxidized natural graphite and soft carbon, and the mass ratio is controlled as the mass of the natural graphite: hard carbon quality: the mass of the soft carbon is 80-98: 1-10: 1-10.
The high-performance lithium ion battery graphite cathode material controls the particle size of the high-performance lithium ion battery graphite cathode material to be 2-45 um and the specific surface area to be 3-20m2/g。
The solvent is any one of toluene, xylene, quinoline or water.
The soft carbon refers to amorphous carbon which can be graphitized at high temperature; while hard carbon refers to pyrolytic carbon of high molecular polymers.
The inert atmosphere in the present invention refers to the atmosphere condition in the presence of nitrogen and/or helium.
The invention discloses a preparation method of a high-performance graphite cathode material of a lithium ion battery, which adopts surface oxidation treatment of natural graphite to improve the capacity, adopts hard carbon coating to ensure that the graphite cathode material has high-rate charging capability, adopts dipping treatment to repair the defects left after oxidation and hard carbon coating, and improves the cycle performance of the graphite cathode material of the lithium ion battery; when the material is used as a lithium ion battery cathode material, the material has high capacity, high compaction, excellent rate capability and cycle life.
Compared with the prior art, the technical scheme of the invention also has the following beneficial effects:
1. the natural graphite and hard carbon coating are combined, so that the capability density of the graphite cathode material for the lithium ion battery is ensured, and the rate capability of the material is greatly improved;
2. the pressure asphalt solvent impregnation technology is used for repairing the defects left by oxidation of natural graphite and carbonization of hard carbon, and the cycle performance of the graphite cathode material of the lithium ion battery is greatly improved;
3. the prepared graphite cathode material for the lithium ion battery has better cycle performance by adopting a secondary carbonization treatment process, and is charged and discharged at a constant current of 0.2C multiplying power, the lower limit voltage is 0.001V, the upper limit voltage is 2.0V, the first efficiency of the charge and discharge capacity reaches more than 94%, and the cycle capacity retention rate reaches more than 650 mAh/g.
Drawings
FIG. 1: the SEM atlas of the graphite cathode material of the high-performance lithium ion battery prepared by the preparation method is an SEM image of the composite material prepared by one embodiment; shown as SEM spectra for two products;
FIG. 2: the graphite cathode material for the lithium ion battery prepared by the method is a half-battery test pattern of the composite material;
FIG. 3: the graphite cathode material for the lithium ion battery prepared by the method is compared with a charging and discharging curve chart by a common artificial graphite 5C charging 1C discharging cycle test.
The specific implementation mode is as follows:
the present invention will be further described with reference to the following detailed description, and in order to make the technical problems, technical solutions and advantages solved by the present invention more apparent, the present invention will be further described with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The invention relates to a high-capacity high-power graphite cathode material for a lithium ion battery and a preparation method thereof, or a high-performance graphite cathode material for the lithium ion battery and a preparation method thereof, which are composed of oxidized natural graphite coated by hard carbon and surface-modified soft carbon, and the method sequentially comprises the following steps:
1) the oxidation treatment is to fully stir and mix natural graphite and an oxidant with an aqueous solution of oxalic acid and sodium persulfate or a mixed solution of sodium peroxide and concentrated sulfuric acid, filter, dry and carry out high-temperature oxidation treatment under the condition of inert atmosphere to obtain oxidized natural graphite; controlling the mass ratio of the natural graphite to the peroxide and the organic acid or the natural graphite to the peroxide salt and the inorganic acid to be 80-95: 5-20: 1-10; controlling the temperature of the high-temperature oxidation treatment to be 500-600 ℃; the time is 2-4 h; preferably the oxidizing agent is a mixture of sodium persulfate and oxalic acid;
2) preparing a graphite cathode material precursor, placing the oxidized natural graphite in the step 1) into a coating agent and a corresponding solvent, fully stirring and mixing to obtain a mixture of the oxidized natural graphite and the coating agent, wherein the coating agent is one or more of sucrose, phenolic resin, epoxy resin and polyvinyl alcohol which are dissolved in the corresponding solvent and mixed, and the mass ratio of the oxidized natural graphite to the coating agent is controlled to be 100: 3-40; spray drying the mixture of the oxidized natural graphite and the coating agent to obtain a graphite cathode material precursor;
3) performing low-temperature carbonization treatment, namely performing low-temperature carbonization treatment on the graphite cathode material precursor obtained in the step 2) in an inert atmosphere to obtain a carbonized graphite cathode material precursor; the temperature of the low-temperature carbonization treatment is controlled to be 500-650 ℃, the time is 6-20h, and the temperature rise rate of the low-temperature carbonization is controlled to be 5-8 ℃/min.
4) The pitch dipping treatment, namely placing the carbonized graphite anode material precursor in a pitch solvent, mixing and dissolving under the condition of pressure, taking out, filtering and drying to obtain the pitch carbonized graphite anode material precursor; controlling the asphalt to be low-temperature asphalt or medium-temperature asphalt; controlling the pressure to be 0.2-1.5Mp, and keeping the pressure for 0.2-3h under the condition that the pressure exists;
5) performing secondary carbonization to prepare a graphite cathode material for a high-performance lithium ion battery, crushing the pitch carbonized graphite cathode material precursor material obtained in the step 4), and performing high-temperature carbonization treatment in an inert atmosphere, wherein the particle size of the crushed material of the pitch carbonized graphite cathode material precursor material is controlled to be 1-50 um, the high-temperature carbonization temperature is controlled to be 1200-1400 ℃, and the carbonization time is 5-24 h; controlling the heating rate of high-temperature carbonization to be 4-10 ℃/min; thus obtaining the graphite cathode material for the high-performance lithium ion battery.
Preferably, the natural graphite mass in the step 1): oxalic acid: the mass of the sodium persulfate is 80-95: 5-20: 1-10, the treatment temperature is 500-;
preferably, the mass of graphite in the step 2): the mass of the coating agent is 100: 3-40;
preferably, the high-temperature carbonization temperature curve in the step 3) is as follows: the heating rate is 1-10 ℃/min, the sintering temperature is 500-900 ℃, and the sintering time is 5-24 h;
preferably, the solvent is any one of toluene, xylene, quinoline or water;
finally, the final product, namely the high-capacity and high-power graphite negative electrode material for the lithium ion battery, is prepared by the method, wherein the particle size of the graphite negative electrode material is 2-45 um, and the specific surface area is 3-20m2Per g, wherein the mass of the natural graphite is as follows: hard carbon quality: the mass of the soft carbon is 80-98: 1-10: 1-10.
The graphite cathode material for the high-performance lithium ion battery prepared by the method has the advantages that the natural graphite is subjected to surface oxidation treatment to improve the capacity, the graphite cathode material has high-rate charging capacity due to hard carbon coating, the defects left after oxidation and hard carbon coating are repaired by dipping treatment, and the cycle performance of the graphite cathode material is improved. When the material is used as a negative electrode material of a lithium ion battery, the material has high capacity, high compaction, excellent rate capability and cycle life.
Example 1:
the invention relates to a high-capacity high-power graphite cathode material for a lithium ion battery and a preparation method thereof, which is composed of oxidized natural graphite coated with hard carbon and surface-modified soft carbon, and the method sequentially comprises the following steps:
1) the oxidation treatment is to fully stir and mix the natural graphite and the mixed solution of the oxidant, oxalic acid and the aqueous solution of sodium persulfate, filter, dry and carry out high-temperature oxidation treatment under the condition of inert atmosphere to obtain oxidized natural graphite; the mass ratio of the prepared natural graphite to the peroxide and the organic acid or the natural graphite to the peroxide salt and the inorganic acid is 80-95: 5-20: 1-10; controlling the temperature of the high-temperature oxidation treatment to be 500-600 ℃; the time is 2-4 h; preferably the oxidizing agent is a mixture of sodium persulfate and oxalic acid;
2) preparing a graphite cathode material precursor, placing the oxidized natural graphite in the step 1) into a coating agent and a corresponding solvent, fully stirring and mixing to obtain a mixture of the oxidized natural graphite and the coating agent, wherein the coating agent is one or more of sucrose, phenolic resin, epoxy resin and polyvinyl alcohol which are dissolved in the corresponding solvent and mixed, and the mass ratio of the oxidized natural graphite to the coating agent is controlled to be 100: 3-40; spray drying the mixture of the oxidized natural graphite and the coating agent to obtain a graphite cathode material precursor;
3) performing low-temperature carbonization treatment, namely performing low-temperature carbonization treatment on the graphite cathode material precursor obtained in the step 2) in an inert atmosphere to obtain a carbonized graphite cathode material precursor; the temperature of the low-temperature carbonization treatment is controlled to be 500-650 ℃, the time is 6-20h, and the temperature rise rate of the low-temperature carbonization is controlled to be 5-8 ℃/min.
4) The pitch dipping treatment, namely placing the carbonized graphite anode material precursor in a pitch solvent or a pitch organic solution to carry out mixing and dissolving treatment under the condition of pressure, taking out, filtering and drying to obtain the pitch carbonized graphite anode material precursor; controlling the asphalt to be low-temperature asphalt or medium-temperature asphalt; the organic solvent is any one of toluene, xylene and quinoline; controlling the pressure to be 0.2-1.5Mp, and keeping the pressure for 0.2-3h under the condition of pressure existence;
5) performing secondary carbonization to prepare a graphite cathode material for a high-performance lithium ion battery, crushing the pitch carbonized graphite cathode material precursor material obtained in the step 4), and performing high-temperature carbonization treatment in an inert atmosphere, wherein the particle size of the crushed material of the pitch carbonized graphite cathode material precursor material is controlled to be 1-50 um, the high-temperature carbonization temperature is controlled to be 1200-1400 ℃, and the carbonization time is 5-24 h; controlling the heating rate of high-temperature carbonization to be 4-10 ℃/min; the graphite cathode material for the high-performance lithium ion battery is obtained, and the components of the graphite cathode material for the high-performance lithium ion battery are controlled to be natural graphite in mass: hard carbon quality: the mass of the soft carbon is 80-98: 1-10: 1-10.
Specifically, the method comprises the steps of 1) adding 1000g of natural graphite into 1000ml of water for oxidation treatment, adding 10g of sodium persulfate and 50g of oxalic acid to form a mixed aqueous solution, stirring for 1-2h at the temperature of 60 ℃, filtering, carrying out vacuum drying for 18-24h, placing in a box-type furnace of a heating device under the protection of nitrogen atmosphere, heating to 600 ℃, carrying out heat preservation for 3h, naturally cooling, taking out, and marking as material A, namely weighing material A under the oxidized natural graphite; 2) preparing a graphite cathode material precursor, dissolving 50g of sucrose as a coating agent in 2000L of deionized water, adding 1000g of the material A, spray-drying to obtain a precursor, namely the graphite cathode material precursor, 3), carbonizing at low temperature, placing the graphite cathode material precursor obtained in the step 2) into a box-type furnace, heating to 650 ℃ at a heating rate of 5 ℃/min under the protection of nitrogen atmosphere, preserving heat for 6 hours, naturally cooling, and taking out to obtain a carbonized graphite cathode material precursor, and marking as a material B; 4) preparing a 10 mass percent low-temperature asphalt toluene solution, placing the solution into a high-pressure kettle, adding a material B, increasing the pressure of the reaction kettle to 1.5Mp under the condition of inert gas, maintaining the pressure for 1h under the condition of the pressure, taking out the material, filtering and drying to obtain a precursor of the asphalt carbonized graphite cathode material, namely a material C;
5) and (2) performing secondary carbonization, namely crushing the material C to 18um after the particle size of D50 is 18um, placing the material C in a box-type furnace, heating to 1200 ℃ at a heating rate of 5 ℃/min under the protection of nitrogen atmosphere, preserving heat for 5h, cooling, taking out to obtain a target product, namely the graphite cathode material for the high-performance lithium ion battery, and controlling the mass ratio of the prepared graphite cathode material for the high-performance lithium ion battery to be natural graphite: hard carbon quality: the mass of the soft carbon is 80-98: 1-10: 1-10. The SEM pictures are shown in figure 1, and the two pictures in figure 1 are SEM pictures of two products prepared by the preparation method.
The following are lithium ion battery performance tests made of the high-performance lithium ion battery graphite cathode material prepared by the method of the invention, and the active materials, namely the lithium ion battery graphite cathode material prepared by the method of the invention, a conductive agent, super P carbon black, sodium carboxymethylcellulose (CMC) and Styrene Butadiene Rubber (SBR): deionized water is stirred for 3 hours at a speed of 2600r/min with a mass ratio of 85:12:6:5:100, 2000-: such as 1.2-1.6mol/L lithium hexafluorophosphate (LiPF 6)/Ethylene Carbonate (EC): dimethyl carbonate (DMC): the Ethyl Methyl Carbonate (EMC) is a mixture of 12:12: 76.
The battery prepared by the invention is subjected to charge and discharge tests, constant current charge and discharge are carried out under 0.2C multiplying power, the lower limit voltage is 0.001V, and the upper limit voltage is 2.0V. The charge and discharge curves are shown in figure 2. The charge and discharge capacities were first efficiency, respectively. The battery is subjected to a multiplying power charge-discharge cycle test, and the cycle capacity retention rate of the battery is shown in a curve figure 3. The following examples are the same as example 1 except for the description in the examples.
Example 2:
adding 1000g of natural graphite into 1000ml of water, adding 10g of sodium persulfate and 50g of oxalic acid aqueous solution, stirring for 2h at 60 ℃, filtering, vacuum drying for 24h, placing in a box furnace under nitrogen atmosphere, heating to 600 ℃ at the heating rate of 6 ℃/min, keeping the temperature for 3h, cooling, taking out, marking as material A, dissolving 30g of coating agent phenolic resin into 1500ml of absolute ethyl alcohol, adding material A, spray drying to obtain a precursor, placing the precursor in the box furnace, heating to 800 ℃ at the heating rate of 2 ℃/min under nitrogen atmosphere, keeping the temperature for 3h, marking as material B, preparing 10 mass percent of asphalt toluene solution, placing in a high-pressure reaction kettle, adding material B, increasing the pressure of the reaction kettle to 1.5Mp, keeping the pressure for 1h, taking out the material, filtering and drying (marking as material C), crushing the material C to obtain D50 particle size, placing in the box furnace, under the protection of nitrogen atmosphere, raising the temperature rise rate to 1200 ℃ at the speed of 2 ℃/min, preserving the heat for 5h, reducing the temperature and taking out to obtain the target product which is the high-performance lithium ion battery graphite cathode material. Button cell assembly and testing were the same as example 1.
Example 3:
adding 1000g of natural graphite into 1000ml of water, adding 10g of sodium persulfate and 50g of oxalic acid, stirring for 2h at 60 ℃, filtering, vacuum drying for 24h, placing in a box furnace under nitrogen atmosphere, heating to 600 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 3h, cooling, taking out, marking as material A, dissolving 40g of polyvinyl alcohol into 1000ml of water, adding material A, spray drying to obtain a precursor, placing the precursor in the box furnace, heating to 900 ℃ at the heating rate of 2 ℃/min under nitrogen atmosphere, keeping the temperature for 3h (marking as material B), preparing an asphalt xylene solution with the mass concentration of 10%, adding material B, increasing the pressure of the reaction kettle to 1.2Mp, keeping the pressure for 1h, taking out the material, filtering and drying, marking as material C, crushing the material C into D50 with the particle size of 18um, placing in the box furnace, heating to 1300 ℃ at the heating rate of 8 ℃/min under the protection of nitrogen atmosphere, preserving heat for 5h, cooling and taking out to obtain the target product.
Example 4:
adding 1000g of natural graphite into 1000ml of water, adding 10g of sodium persulfate and 50g of oxalic acid, stirring for 2h at 60 ℃, filtering, vacuum drying for 24h, placing in a box furnace under nitrogen atmosphere, heating to 600 ℃ at the heating rate of 5 ℃/min, keeping the temperature for 3h, cooling, taking out, marking as material A, dissolving 50g of aqueous epoxy resin into 1500ml of water, adding material A, spray drying to obtain a precursor, placing the precursor in the box furnace, heating to 800 ℃ at the heating rate of 2 ℃/min under nitrogen atmosphere, keeping the temperature for 3h, marking as material B, preparing an asphalt toluene solution with the mass concentration of 15%, placing in a high-pressure reaction kettle, adding material B, increasing the pressure of the reaction kettle to 1.2Mp, keeping the pressure for 1h, taking out the material, filtering, drying and marking as material C, crushing the material C into D50 with the particle size of 15um, placing in the box furnace, heating at the heating rate of 7 ℃/min to 1400 ℃ under the protection of helium atmosphere, preserving heat for 5h, cooling and taking out to obtain the target product. Button cell assembly and testing were the same as example 1.
Example 5:
the invention relates to a high-capacity high-power graphite cathode material for a lithium ion battery and a preparation method thereof, which is composed of oxidized natural graphite coated with hard carbon and surface-modified soft carbon, and the method sequentially comprises the following steps:
1) adding 1000g of natural graphite into 1000ml of water, adding 10g of sodium persulfate and corresponding sulfuric acid to form a mixed aqueous solution, stirring for 1-2h at the temperature of 70 ℃, filtering, performing vacuum drying for 18-24h, placing in a box furnace of a heating device under the protection of nitrogen atmosphere, heating to 500 ℃, preserving heat for 2h, naturally cooling, taking out, and marking as material A, namely weighing material A under the oxidized natural graphite; 2) preparing a graphite cathode material precursor, dissolving 50g of epoxy resin serving as a coating agent into 2000L of deionized water, adding 1000g of a material A, and controlling the mass ratio of the oxidized natural graphite to the coating agent to be 100: 3-40; the method comprises the following steps of (1) preparing a mixture of natural graphite oxide and a coating agent, spray-drying the mixture of the natural graphite oxide and the coating agent to obtain a precursor, namely a graphite cathode material precursor, (3) carbonizing at low temperature, placing the carbonized graphite cathode material precursor obtained in the step 2) into a box-type furnace, heating to 500 ℃ at a heating rate of 6 ℃/min under the protection of nitrogen atmosphere, keeping the temperature for 6 hours, cooling, and taking out to obtain the carbonized graphite cathode material precursor, and marking as a material B; 4) preparing a medium-temperature asphalt toluene solution with the mass concentration of 10%, placing the medium-temperature asphalt toluene solution into a high-pressure kettle, adding a material B, increasing the pressure of the reaction kettle to 1.0Mp under the condition of inert gas, maintaining the pressure for 2 hours, taking out the material, filtering and drying to obtain a precursor of the asphalt carbonized graphite cathode material, namely a material C;
5) and (2) performing secondary carbonization, namely crushing the material C to 25um after the particle size of D50 is reduced, placing the material C in a box-type furnace, heating to 1300 ℃ at a heating rate of 4 ℃/min under the protection of nitrogen atmosphere, preserving heat for 10h, cooling, taking out to obtain a target product, namely the graphite cathode material for the high-performance lithium ion battery, and controlling the mass ratio of the prepared graphite cathode material for the high-performance lithium ion battery to be natural graphite quality: hard carbon quality: the mass of the soft carbon is 80-98: 1-10: 1-10.
The high-performance lithium ion battery graphite cathode material prepared by the method has the advantages that the capacity is improved by surface oxidation treatment of natural graphite, the capacity is increased by hard carbon coating, the high-rate charging capability is realized by asphalt impregnation treatment, the defects left after oxidation and hard carbon coating are repaired, and the cycle performance is improved. When the material is used as a lithium ion battery cathode material, the material has high capacity, high compaction, excellent rate capability and cycle life.
Claims (3)
1. A preparation method of a high-performance lithium ion battery graphite cathode material takes natural graphite as a raw material, improves capacity through oxidation treatment, improves multiplying power performance through hard carbon coating, and improves cycle performance through dipping treatment, and is characterized by comprising the following steps:
1) the oxidation treatment is to fully stir and mix the natural graphite and the oxidant mixed solution, filter, dry and carry out high-temperature oxidation treatment under the condition of inert atmosphere to obtain oxidized natural graphite;
2) preparing a graphite cathode material precursor, putting the oxidized natural graphite in the step 1) into a coating agent and a corresponding solvent, fully stirring and mixing to obtain a mixture of the oxidized natural graphite and the coating agent, and spray-drying the mixture of the oxidized natural graphite and the coating agent to obtain the graphite cathode material precursor;
3) performing low-temperature carbonization treatment, namely performing low-temperature carbonization treatment on the graphite cathode material precursor obtained in the step 2) in an inert atmosphere to obtain a carbonized graphite cathode material precursor;
4) the pitch dipping treatment, namely placing the carbonized graphite anode material precursor in a pitch solvent, mixing and dissolving under the condition of pressure, taking out, filtering and drying to obtain the pitch carbonized graphite anode material precursor;
5) performing secondary carbonization to prepare a graphite cathode material for the high-performance lithium ion battery, crushing the pitch carbonized graphite cathode material precursor material obtained in the step 4), and performing high-temperature carbonization treatment in an inert atmosphere to obtain the graphite cathode material for the high-performance lithium ion battery;
the oxidant in the step 1) is a mixture of peroxide and organic acid or a mixture of peroxide and inorganic acid, and the mass ratio of the natural graphite to the peroxide to the organic acid or the natural graphite to the peroxide to the inorganic acid is controlled to be 80-95: 5-20: 1-10; controlling the temperature of the high-temperature oxidation treatment to be 500-600 ℃; the time is 2-4 h;
the coating agent in the step 2) is one or more of sucrose, phenolic resin, epoxy resin and polyvinyl alcohol; controlling the mass ratio of the oxidized natural graphite to the coating agent to be 100: 3-40;
step 3), controlling the low-temperature carbonization treatment temperature to be 500-650 ℃, the time to be 6-20h, and controlling the heating rate to be 5-8 ℃/min;
step 4), performing asphalt impregnation treatment, wherein the asphalt is low-temperature asphalt or medium-temperature asphalt; controlling the pressure to be 0.2-1.5Mpa, and keeping the pressure for 0.2-3h under the condition of pressure existence;
step 5), controlling the particle size of the crushed material of the pitch carbonized graphite anode material precursor material to be 1-50 mu m, controlling the high-temperature carbonization temperature to be 1200-1400 ℃, and controlling the carbonization time to be 5-24 h; controlling the temperature rise rate of high-temperature carbonization to be 4-10 ℃/min.
2. The method for preparing the graphite cathode material of the high-performance lithium ion battery according to claim 1, wherein the oxidant is a mixture of sodium persulfate and oxalic acid or a mixture of sodium peroxide and concentrated sulfuric acid.
3. The graphite cathode material for the high-performance lithium ion battery, which is prepared by the preparation method of the graphite cathode material for the high-performance lithium ion battery according to claim 1, is characterized in that the graphite cathode material for the high-performance lithium ion battery is formed by coating natural graphite oxide and soft carbon with hard carbon, and the mass ratio is controlled as the mass of the natural graphite: hard carbon quality: the mass of the soft carbon is 80-98: 1-10: 1-10;
the particle size of the graphite cathode material for the high-performance lithium ion battery is controlled to be 2-45 mu m, and the specific surface area is controlled to be 3-20m2/g。
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